Wimmera River near Dimboola, Victoria Summary of WIMMERA–AVOCA REGION From the Guide to the proposed Basin Plan This publication summarises proposals outlined in the Guide to the proposed Basin Plan as they relate to the Wimmera-Avoca region. THE REGION The Wimmera–Avoca region is comprised of the major surface- water catchments of the Wimmera and Avoca rivers and includes the major townships of Horsham, Stawell, Ouyen, Charlton, St Arnaud and Avoca. To the south-west, the region is bound by the Grampians, where rainfall feeds the tributaries of the Wimmera River, with the Pyrenees in the south-east. The northern areas of the region include the dunefields of the Little Desert to the west, and the riverine floodplains of the Avoca River. The major watercourses in the region flow north from the Grampians and flow into terminal lakes rather than draining into the River Murray. The Wimmera River has headwaters across the Grampians to the south and Pyrenees in the south-east. It flows west through the town of Horsham and then north to terminate in lakes Hindmarsh and Albacutya. The Avoca River flows north from its Wimmera-Avoca Region surface water Current headwaters in the central highlands into Lake Diversion Limit (GL/y) Bael Bael then through the Avoca Marshes Interceptions Watercourse diversions Total and the Avoca outfall floodplain. Under flood 62 74 136 conditions flows may enter Lake Boga via a diversion channel, which in turn under high floods can discharge to the Little Murray River. Dryland agriculture is the dominant land use in the Wimmera–Avoca region, dominated Water USE AND environmentaL HEALTH by broadacre cropping of cereals, oilseed, The Authority has compiled the current limits pulses and hay. for all forms of water extraction in the Murray- Prior to commissioning of the Wimmera Mallee Darling Basin. For surface water these current Pipeline, surface-water was primarily used for diversion limits include watercourse diversions stock and domestic uses, and was delivered to for town and community water supplies, farm dams by the domestic and stock channel irrigation and industries, floodplain harvesting, supply system. Around 17% of surface-water and interception activities such as farm dams was supplied to urban centres and small and forestry plantations. For groundwater they volumes were used for irrigation. include all water diverted from the aquifers Irrigation is currently limited to small areas of the area. Current diversions are limited by (approximately 3,000 ha) near Horsham and existing transitional and interim water resource Murtoa in the Wimmera catchment, and a small plans where these are in place. These are area of the Avoca catchment north-west of existing plans, prepared by Basin states, and the Loddon River, near Swan Hill. The largest recognised under the Water Act 2007 (Cwlth) number of agricultural businesses irrigating in (the Act). Where there are no existing plans, the Wimmera catchment are grape producers or plans do not apply to certain types of water extracting water from upper catchment dams. extraction, the current diversion limit reflects the current level of use. There are a number of factors indicating very poor ecological condition in the Wimmera- The surface water long-term average current Avoca region. For example: Remnant vegetation diversion limit for the Basin as a whole has cover is very poor throughout the catchment been estimated at around 13,700 GL/y and at and along watercourses. Only a small 136 GL/y for the Wimmera-Avoca region. The proportion of expected native fish species are Basin wide groundwater long-term average present. Native fish species are abundant in current diversion limit is 1,786 GL/y. the Wimmera and depleted in the Avoca but in both catchments alien species dominate the biomass. The hydrological condition for the Wimmera valley is poor, but moderate to good for the Avoca. Stream condition is moderate or poor and macroinvertebrate diversity is low. The primary water quality issue in the Wimmera region is high salinity levels due to saline groundwater intrusion. ASSESSING environmentaL water NEEDS Many of the environmental assets and functions of the Murray-Darling Basin have been degraded by the over-extraction of water from the Basin’s rivers. The Act and Basin Plan seek to address the over- Irrigated grapevines near Lake Boga, Victoria extraction of water to restore and maintain SUStainaBLE DIVERSION LIMIT ProPOSALS the Basin’s key environmental assets and key AT THE BASIN AND REGIONAL SCALE ecosystem functions. The Authority is required to establish new To determine sustainable diversion limit (SDL) long-term average SDLs for surface water proposals it is necessary to work out how much and groundwater. SDLs represent the long- water is needed to sustain the health of the term average amount of water which can be Basin’s river systems, wetlands and floodplains. used for consumptive purposes after meeting To do this, the Authority has undertaken the environmental water needs that have an assessment of the environmental water been identified. requirements of key environmental assets and In the Guide, the Authority presents the SDLs key ecosystem functions across the Murray- as a range of scenarios for discussion at this Darling Basin. In the most part, the assets stage, rather than choosing a particular value in assessed are large flood-dependent wetland this range. This range takes into account all the and floodplain systems that support populations available evidence, the quality of that evidence, of waterbirds and fish, and large forests and and the inherent uncertainty of modelling. woodlands. The assessment of key ecosystem functions gave particular attention to the The Authority has determined that 3% of the environmental water requirements of rivers, current diversion limit (around 410 GL/y for and system wide processes such as connectivity the Basin as a whole and around 4 GL/y for between rivers and floodplains. the Wimmera-Avoca region) is an appropriate allowance to account for the effect of climate Together, these assessments included specific change on surface water SDL proposals. The analysis of flows at 106 hydrologic indicator SDL proposals for groundwater do not include a sites across the Basin (88 sites to assess the climate change component. water needs for the Basin’s key ecosystem functions and 18 to assess the water needs for The SDL proposals would require a reduction key environmental assets), as well as analysis in the current long-term average surface water of end of system flows in each region. diversion limit at the Basin scale from 13,700 GL per year to between 10,700 GL and 9,700 GL The environmental water requirements at a per year (reduction between 3,000 GL and 4,000 Basin scale have been estimated between GL per year or 22% to 29%). 22,100 GL/y and 26,700 GL/y (an increase between 3,000GL/y to 7,600GL/y from the 19,100 Reductions in surface water current diversion GL/y currently available for the environment). limits for the Wimmera-Avoca region are not proposed. In the Wimmera-Avoca region, 82 key environmental assets have been identified. Of The SDL proposals would also required a the 106 hydrological indicator sites across the reduction in the current long-term average Basin the Wimmera-Avoca region contains 3 groundwater diversion limit at the Basin scale hydrological indicator sites for key ecosystem by an aggregate 186 GL or an average reduction functions and 1 hydrologic indicator site for key of 10% across the Basin. The reductions in environmental assets. This is the Wimmera current diversion limits are required in only 11 River Terminal Wetlands. of the 78 groundwater SDL areas. No reductions are proposed for the remaining 67 groundwater The environmental water requirements for the SDL areas where the current diversions are Wimmera-Avoca region have been estimated at assessed as sustainable. 323 GL/y (323 GL/y are currently available for the environment). SDL proposals for the surface water and groundwater SDL areas of the Wimmera-Avoca Further information on assessing the region are set out on page 5. environmental water requirements of the Basin is available at http://www.mdba.gov.au/basin_ plan/water-assessment-report. SUPPorting commUNITIES The Murray–Darling Basin Authority acknowledges that implementing SDLs may have significant social and economic implications for individual entitlement holders and communities across the Basin. However, the Australian Government has committed to recovering sufficient water access entitlements to fully offset the impact of SDLs across the Basin, including the Wimmera- Avoca region. This will be achieved through a combination of purchasing entitlements in the market and investments in more efficient irrigation infrastructure. Consequently, should these targets be met, there are likely to be no reductions in individual Inspecting harvested nectarines near Nyah, Victoria water entitlement holder allocations. For further information about these activities go to www.environment.gov.au/water. SUSTAINABLE DIVERSION LIMIT PROPOSALS WIMMERA–AVOCA REGION SURFACE WATER GROUNDWATER There is one surface-water SDL area in There are three groundwater SDL areas wholly or partly contained within the the Wimmera-Avoca region. Wimmera-Avoca region. 1) Wimmera-Mallee 1) West Wimmera Current diversion limit 136 GL/y Current diversion limit 2.7 GL/y SDL proposal 136 GL/y SDL proposal 2.7 GL/y Reduction Nil Reduction Nil - potential for unassigned water 2) Wimmera-Avoca Highlands Current